Description of problem:
When a admin selects the Base Channel tab from the Channels tab in the SSM an internal server error results. tomcat throws this error in catalina.out:
2010-04-28 14:53:28,723 [TP-Processor9] ERROR com.redhat.rhn.frontend.servlets.SessionFilter - Error during transaction. Rolling back
javax.servlet.ServletException
...
org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
       at com.redhat.rhn.frontend.servlets.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:97)
...
Caused by:
java.lang.NullPointerException
       at com.redhat.rhn.manager.channel.ChannelManager.listCompatibleBaseChannelsForChannel(ChannelManager.java:2108)
       at com.redhat.rhn.frontend.action.channel.ssm.BaseSubscribeAction.setupList(BaseSubscribeAction.java:364)
       at com.redhat.rhn.frontend.action.channel.ssm.BaseSubscribeAction.unspecified(BaseSubscribeAction.java:105)
       at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:249)
       at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:187)
       at org.apache.struts.actions.LookupDispatchAction.execute(LookupDispatchAction.java:150)
       at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
       ... 40 more
2010-04-28 14:53:28,731 [TP-Processor9] ERROR org.apache.catalina.core.ContainerBase.[Catalina].[localhost].[/rhn].[action] - Servlet.service() for servlet action threw exception
java.lang.NullPointerException
       at com.redhat.rhn.manager.channel.ChannelManager.listCompatibleBaseChannelsForChannel(ChannelManager.java:2108)
       at com.redhat.rhn.frontend.action.channel.ssm.BaseSubscribeAction.setupList(BaseSubscribeAction.java:364)
       at com.redhat.rhn.frontend.action.channel.ssm.BaseSubscribeAction.unspecified(BaseSubscribeAction.java:105)
       at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:249)
       at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:187)
       at ...

Version-Release number of selected component (if applicable):
Red Hat Network (RHN) Satellite 5.3.0

How reproducible:
For customer, consistently with an admin that only has privs to certain custom base channels and groups

Steps to Reproduce (from customer):
1. For a normal user, with no roles we get the error when clicking on the Base Channels tab under the Channels tab. When I give that user either the Channel Administrator or the Organization Administrator role the ISE does not occur. This admin has been selected as a Manager and a Subscriber to a number of Custom base channels (cloned from Red Hat Base channels) of different OS levels and archs.
2. This error was generated with just one system in the SSM. The one system in the SSM is an AS4, i386 system. The channel it is subscribed to and the channel he would be moving to are both cloned base channels, cloned from Red Hat base channels. He is a manager and subscriber to both these channels. The system is in the group that has access to (obviously).

Actual results:
Internal Server Error

Expected results:
Display the base channel choices available to this administrator based on their permissions.

Additional info:
I've not been able to reproduce internally but based on the line numbers did find a missing null check in spacewalk-java-0.5.44/code/src/com/redhat/rhn/manager/channel/ChannelManager.java
...
           Channel c = ChannelFactory.lookupByIdAndUser(ecd.getId().longValue(), u);
           log.debug("   " + c.getName());
...
the log.debug line doesn't have a null check for the Channel c, not to mention also missing a if-debug-enabled check. Partha has already checked in a patch to spacewalk - http://git.fedorahosted.org/git/?p=spacewalk.git;a=commit;h=4a12466c39a4f963d3f554876c46f4ea7edce08a